1. Field of the Invention
The present invention relates to a method for the production of powder with high tannin content, powder with high tannin content obtained by the same method, and a use thereof. More specifically, the present invention relates to a method for the production of powder with high tannin content in an adhesive or a binder for wood as a main component, molding, a binder for molding, a filler an enhancer, a health-care food and a drug.
2. Description of the Related Art
Various components are widely present in plants. It is known that extraction of such components with solvents such as water, aqueous solvents and lower alcohols can give rise to a substance usually called tannin that can be used as an adhesive, a binder, a drug or the like.
In the case where tannin is used as a raw material of adhesives, binders or moldings, plant resources with much tannin contents, for example, bark or wood of mangrove, acacia, radiata pine (Pinus radiata), pine, larch, quebracho, eucalyptus, oak, or Japanese hemlock are crushed to a suitable particle size. Then, tannin is extracted therefrom with water, an aqueous solvent or organic solvent such as a lower alcohol and filtered. The tannin filtrate is concentrated and then used as high concentration tannin solutions or it is dried and then used as powdered tannin.
To efficiently extract tannin, it is advantageous to crush plant resources into particles as small as possible so that an extraction solvent can sufficiently and speedily penetrate into the substances to be extracted, i.e., the plant resources. Although the particle size distribution of plant resources after crushing may be different depending on the kind of plant resource, such as bark, it has been known that a filter having a pore diameter of 20 to 60 μm is suitable for the filtration of tannin solutions in a filtration step after the extraction. However, use of such a filter could in some cases result in formation of a large amount of fine powder that is so fine as to cause the problem of clogging of the filter, so that efficient filtration cannot be performed.
Conventionally, the extraction has been performed after removing the fine particles obtained after the pulverization. However, mere removal of the fine particles not only results in a great loss of raw material but also raises a problem of causing environmental pollution when they are discarded.